There are a few different methods to manufacture steel pipe, and depending on your application, one will probably suit your needs better than the others.
Furnace (Continuous) Weld (FW): The beginning of this process includes a coiled skelp that is a specific measurement so that the tube can be reduced and made to the desired size. Coils are welded at the ends to create an ongoing ribbon of steel. Once you have this coiled steel, the product is fed into a roller leveler followed by a gas fired furnace. In the furnace, the pipe is heated to a degree so high that it is then formed and welded into the correct size. Once the piece is fed through, the forming rolls at the exit shape the product into a skelp that has an oval shape that is open at the bottom, which is where the weld will be located. The product is then passed through another set of rolls that press the two edges together in order to acheive a fusion weld. The piece is then passed through another set of rolls on the mill, in which the diameter of the pipe is finished to the set size. As the pipe emerges from the last roll, a flying cut off saw is then used to cut the pipe into double lengths, then by a rotary saw to single lengths. This process allows the pipe to be finished with any ends needed, as well as an assortment of surface finishes. This particular process is designated “Type F” in ASTM and API specifications.
Electric Resistance Weld Pipe (ERW): Pipe that is produced either from continuous rolls of skelp or from individual sheets. In contrast to the FW, ERW pipe is cold formed into shape as opposed to the hot form that the FW uses. An electric current is also used to heat the edges of the strip for the weld process, and the weld is on the top of the pipe instead of the bottom. This type of pipe is used primarily for the transmission of gases and liquids, but can also be used for various structural applications.
Double Submerged Arc Weld (DSAW): Double Submerged Arc Weld is derived from a Submerged Arc Weld process. SAW is given this name because while the welding is taking place, the welding arc is dipped in flux. The flux is a material that protects the weld seam from obtaining any impurities, but it only protects the pipe when it is heated to the correct welding temperature.
Differing from the original Submerged Arc Weld, the DSAW process occurs when the welds on the inside and outside are created. This can only occur in two separate processes. Part of the inside and outside welds become one, and consume each other, resulting in a single high quality penetration nugget. The double submerged arch weld is much more common because it has a far superior reliability and strength. DSAW pipe gains extra strength during the cold expansion process.
The two processes that we use to form DSAW pipe are known as The Pyramid Rolls Method and the U-O-E Method. The first method begins with three rolls that are formed into a pyramid and these rolls form the cylinder before welding. This process creates pieces that are between 4’-41’. The second process uses a three step process. The first step is a “U” press followed by an “O” press that simultaneously creates the cylindrical form desired. The final is the “E” press, which is when the material is further processed, which is the most known process for the DSAW material. The material created from this process are usually made in double random lengths, and can be finished with whatever ends the customer desires.
Seamless (SMLS): The seamless pipe process is much different from any other manufacturing process because it has no welds or seams. The pipe starts as a solid steel billet, and is then heated and placed over a piercing point which creates a steel shell. The process is finished further once the initial shell is created, and is then molded into the desired diameter and wall thickness. The pipe created from this process is made in a heated application, so the pipe should be fully normalized and have a consistent cellular pattern throughout the entire circumference of the material.
Spiral Weld (SPRL): A spiral weld manufacturing process is created with a spiral seam running down the entire length of the pipe. Spiral weld used to be used only for applications of low pressure and structural requirements, but because the process has been perfected, it can now be used for higher pressure applications. There are a few different devices that are required to refine a piece of spiral weld pipe. These devices include: a de-coiling device, straightening rollers, a strip connecting welder, tools that prep the edges, pre-bending devices, a roller bending and cage forming system, welders for internal and external seams, a testing apparatus that is ultra sonic, and a cutting device to finalize the material. This material is normally used for gas and oil transmission, pipelines, slurry jobs, dredging jobs, and other various uses.